Method and apparatus for high frequency electric surgery

ABSTRACT

A method and apparatus for electric surgery includes generating oscillations of high frequency electric energy of substantially constant amplitude, controlling the duration of and spacing in time between each series of oscillations generated and applying the generated energy through an electrode for the purpose of making surgical incisions and coagulating blood at the point of incision. A common generator serves as a source of the electric energy for different surgical procedures, the duration and spacing between each series of oscillations being closely controlled according to their intended application and in such a way as to minimize power requirements and the possible hazards of use either to the doctor or to the patient.

United States Patent Sittner 1 July 11, 1972 METHOD AND APPARATUS FOR HIGH FREQUENCY ELECTRIC SURGERY Weldon Rex Sittner, Westport. Conn.

Electro Medical Systerm, lnc., Englewood. Colo.

Filed: Feb. 4. I970 Appl. No.: 8,549

Inventor:

Assignee:

References Cited UNITED STATES PATENTS GND POWER SUPPLY CONTROL MULTIVIBRATOP FOREIGN PATENTS OR APPLICATIONS 897.961 6/1962 GreatBritain ....l28/303.|4 1.146.989 4/1963 Germany ..l28/303.l4

Primary Examiner-Channing L. Pace Armrney-Philip G. Hilbert ABSTRACT A method and apparatus for electric surgery includes generating oscillations of high frequency electric energy of substantially constant amplitude. controlling the duration of and spacing in time between each series of oscillations generated and applying the generated energy through an electrode for the purpose of making surgical incisions and coagulating blood at the point of incision. A common generator serves as a source of the electric energy for different surgical procedures, the duration and spacing between each series of oscillations being closely controlled according to their intended application and in such a way as to minimize power requirements and the possible hazards of use either to the doctor or to the patient.

llClaimsJDnwingI igures 101 COAGULATE |L2 B's ii IIIQOS PKTENTEUJUL 1 1 m2 SHEET 3 OF 3 x mm mobamzww n30 xm mm lu l m2 E. m mpzmuzmw PDQ METHOD AND APPARATUS FOR HIGH FREQUENCY ELECTRIC SURGERY This invention relates to medical electronic methods and apparatus, and more particularly to a method and apparatus for conducting electric surgery in a safe and highly effective manner.

Heretofore, devices have been designed which have employed radio-frequency (RF) electric energy for performing surgery on the human body. Typically, such devices included a cutting mode of operation wherein a continuous waveform of RF energy produced by a vacuum the generator was used to cut by means of the heat generated in the body tissue and a coagulation mode wherein a damped RF energy waveform provided by a separate spark-gap type generator was used to coagulate the blood flowing from the cut tissues. A disadvantage with such prior art devices was that in order to perform the cut/coagulation functions, two separate generators were required and which applied extremely high voltages to the active cutting electrode. Consequently, such devices and particularly the spark-gap generator unduly destroyed the tissue and further constituted significant hazards in their use both for the patient and the operating physician.

Accordingly, it is an object of this invention to provide a novel method and apparatus for cutting tissue and coagulating the blood at the area of the cut using the same RF generator and characterized by applying envelopes or packets of RF electric energy in an oscillatory waveform of substantially constant amplitude recurring at preselected spaced time intervals.

Another object of the present invention is to provide a novel apparatus for high frequency electric surgery which obviates the aforementioned disadvantage of prior art instruments by employing electric circuitry which enables the use of substantially lower RF voltages than heretofore possible and provides an essentially unmodulated oscillatory waveform.

It is another object of the present invention to provide novel apparatus for high frequency electric surgery as set forth which is capable of conducting both a cut mode of operation and a coagulation mode of operation, either simultaneously or independently of one another.

It is further an object of the present invention to provide a novel apparatus for high frequency electric surgery characterized by having an RF generator and control circuitry using solid state elements which is highly sensitive, reliable and effcient, and has close power regulation, and is closely adjustable and controllable in carrying out different selected surgical procedures and techniques in a safe dependable manner.

In accomplishing these and other objects, there has been provided in accordance with the present invention electric apparatus for performing high frequency electric surgery which includes an RF generator, and a control multivibrator, asymmetrical in operation, to control the RF generator to provide a combined cut and coagulation mode, and a coagulation mode of operation. Switching means are provided whereby the RF generator may be continuously operated or alternately controlled by the control multivibrator. The RF generator is connected to amplifying means for amplifying the RF power or energy generated by the RF generator and applying it to an active electrode for use in cutting or coagulating living body tissue. A return means in the form of a patient ground plate is positioned against the patient below the area of the body to be operated on for providing a return electric path to the amplifying means. A power supply means supplies relatively low DC voltages to the apparatus circuitry. In this way there is provided by a single electronic oscillator circuit a series of envelopes of RF electric energy in an oscillatory waveform of substantially constant amplitude with the envelopes recurring at selected spaced time intervals for coagulation of blood or combined cutting and coagulation or the energy in a continuous waveform for the usual cutting of body tissue.

A better understanding of the present invention may be had from the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is partially a block diagram and partially a circuit diagram of an electric apparatus for high frequency electric surgery in accordance with the present invention.

FIG. 2 is a circuit diagram of the control multivibrator of FIG. 1.

FIG. 3 is a circuit diagram of the RF generator of FIG. 1.

FIG. 4 is a circuit diagram of the power amplifier of FIG. 1.

FIG. 5 is a circuit diagram of the power supply of FIG. I.

FIG. 6 is in part a plan view of the patient ground plate of FIG. I and in part a circuit diagram of the connection of the patient ground plate into the circuitry of the electric apparatus of FIG. I.

FIG. 7 is an illustration of the output waveforms generated by the apparatus of FIG. 1 in its different modes of operation together with a comparison of waveforms with a typical sparkgap type generator.

Referring now to FIG. I the electrosurgical apparatus in general is shown to include a control multivibrator circuit 10 for controlling an RF generator circuit 20, the output of which is applied to a power amplifier circuit 30 for increasing the power output together with a power supply 40 which generates the DC voltage required by the aforementioned circuits. In FIG. I, the RF generator 20 is shown to have a DC voltage supplied to generator terminals 22 and 23, and generator terminal 24 is connected to ground. The DC voltage applied to the terminals 22 and 23 is derived from the power supply 40 which generates DC voltages on its output tenninals 46 and 48, and output terminal 47 is grounded. A V- voltage, between terminal 47 and ground may be anywhere in the range of 0-180 volts, and is applied to the generator terminal 23 and to terminal 22 through a resistor 28. An RF bypass capacitor 29 is connected between terminal 22 and ground.

The RF generator 20 has a control terminal 21 which is connected to the fixed contact of one set of relay contacts of the relay 101, hereinafter referred to as the cut relay. A lamp L3 located on the control panel is connected across relay 101 to indicate when the apparatus is in the cut mode. The other of the contacts 100 is a dummy contact while the movable contact arm is connected through an on-off switch 102 to ground. Switch 102 is hereinafter referred to as the cut switch and is a toggle type switch located on the control panel. In the open position shown, the cut mode switch 102 is set for cut 2 and in the closed position it is set for cut 1.

Connected also to the generator terminal 21 is the output terminal 11 of the control multivibrator 10. The control multivibrator II) has DC voltage supplied to its terminals I4 and 15, the terminal 14 being at ground, and B voltage from the power supply 40 being supplied via the circuitry of a patient ground plate or indifi'erent electrode 103, to the terminal I5.

The B- voltage generated by the power supply 40 may, for example, be l4 volts. The control multivibrator 10 has the movable contact arm of relay contacts 104 of the relay 105 connected to its terminal 12. Relay 105 serves as the coagulate relay and a lamp L2 located on the control panel is connected across coil 101 to indicate when the apparatus is in the coagulate" mode. The multivibrator terminal 13 is connected to the other fixed contact of the relay contacts 104.

The RF generator 20 is transformer coupled by means of a step-up power transformer l 10 to the power amplifier 30. The generator 20 has its output terminals 25-27 connected to the primary winding of the transformer III). The power amplifier 30 has its input terminals 32, 33a, 33b and 34 connected to the transformer 110. V- and ground are connected to the terminals 31 and 35, respectively, of the amplifier 30 to supply DC power thereto.

The output of the power amplifier 30 is coupled by a transformer 111 to output lines 11-2 and 113. The primary of the transfonner I I1 is connected to amplifier output terminals 36, 37a, 37b and 38. The output lines 112 and 113 are connected across the secondary winding of the transformer III. A resistor 118 is connected between the output lines I 12 and 113 across which is developed the output voltage of the transfonner l I l.

The output line 112 is a shielded line having its shield connected to ground and is connected through DC isolation capacitors 109 and 1 14 and through a terminal connect 50 to an active electrode 115. Terminal connect 50 permits the electrode to be plugged into the control panel of the apparatus. The output line 1 13 is connected through a DC isolation capacitor 116 to the two terminal connects 51 and 52 of the patient ground plate 103. A capacitor 117 is connected between the terminals 51 and 52 for the purpose of preventing a B- voltage from being supplied to the control multivibrator terminal 15 whenever the patient ground plate 103 is not electrically connected to the electrosurgical apparatus at terminals 51 and 52. Connected to the side of the capacitor 117 adjacent the terminal 51 are a grounded capacitor 120 for DC isolation and an RF inductive choke 121 for isolating the power supply 40 from RF energy. A DC isolation capacitor 122 is also connected to the side of the choke 121 to which B- voltage is supplied.

The terminals 51 and 52 are mutually connected to a common point and from that common point are connected through a DC isolation capacitor 123 to the patient ground plate 103. Connected to the side of the capacitor 117 common with the tenninal 52 is one terminal of an RF inductive choke 124. The other terminal of the choke 124 is connected through an RF inductive choke 125 to the ground plate 103. Connected to the side of the capacitor 117 common with the terminal 52 is one terminal of an RF inductive choke 124. The other terminal of the choke 124 is connected through an RF inductive choke 125 to the line 112 and also the movable contact of a switch 127. The switch 127 is preferably a treadle switch and foot-operated by the physician and has fixed contacts I28 and 129, and is used for switching the mode of operation of the electric apparatus between "cut" and coagulate.

The fixed contact 129 of the switch 127 is connected through a diode 135 to the control multivibrator terminal 15. Similarly, the fixed contact 128 of the switch is connected through a diode 136 to the control multivibrator 15. Thus, 3-- voltage may be supplied to the terminal 15 through the electrical path defined by the choke 121, terminals 51 and 52, the choke 124, the switch 127, and the appropriate diode 135 or 136. In this way, the treadle switch 127 cannot actuate the cut or coagulate relays unless the patient plate 103 is plugged into the instrument. A capacitor 137 is also connected from the switch contact 129 to ground.

The electrical means for connecting the patient ground plate 103 to the exemplary electrosurgical apparatus additionally includes terminals 53 and 54, as better illustrated in H6. 6. The terminals 53 and 54 are shorted together and serve to short out a lamp L4 whenever the plate 103 is connected into the above-described exemplary apparatus. Terminals 51-54 are shown in FIG. 6 as mounted on a common plug represented at 55. B- voltage is supplied to the lamp L4 through a resistor 141. Lamp L4 is preferably located on the control panel and lit until the patient plate 103 is electrically plugged into the panel.

Referring now to FIG. 2, the control multivibrator 10 shown includes a conventional flip-flop circuit with transistors TR and TR6 arranged to alternately conduct and cut-ofi' in a repetitive sequence. The bases of transistors TR5 and TR6 are connected to timing capacitors C6 and C5, respectively. A third timing capacitor C30 is connected between one side of capacitor C5 and terminal 12 so that when terminals 12 and 13 are connected by the actuation of relay 105 the total capacitance in one side of the flip-flop circuit is the sum of the capacitance of capacitors C5 and C30 instead of only C5. This shortens the period of conduction of transistor TR5 and thereby changes the duty cycle for the flip-flop circuit. Variable resistors R6 and R7 connected to capacitors C5 and C6, respectively, may also be adjusted to vary the duration of the duty cycle on each side of the flip-flop circuit. Also included in circuit as shown in H6. 2 is a transistor TR7 having its base electrode connected through resistor R10 to the collector of TR5. The emitter-collector junction of transistor TR7 is connected between terminal 11 and grounded terminal 14. In this way when transistor TR5 is conducting, a suitable voltage is applied to the base of transistor TR7 to cause it to conduct between its emitter and base electrodes and in effect connect terminal 11 to ground or zero potential via transistor TR7 which will enable the RF generator to run for a selected time interval when TR5 is conducting and be off when TR5 is cut off during the cut 2" and coagulate" modes when terminal 21 is not grounded via contacts and switch 102 as described more fully hereinafter.

Referring now to FIG. 3 the RF generator circuit 20 is shown to include an RF oscillator circuit 200 transformer coupled by transformer T2 to a conventional driver amplifier circuit 20b. The driver amplifier circuit includes a transistor TR9 and functions to increase the power from the oscillator circuit 20a to the power amplifier circuit 30 and isolates the oscillator circuit therefrom.

The oscillator circuit 20a includes a transistor TRB having its collector connected to a series resonant circuit of capacitor C28 and winding W1 of transformer T2, with winding W1 having one end connected to grounded terminal 24. An RF choke CH5 is connected between the collector and grounded terminal 24 to provide an RF load for TR8. The emitter of transistor TR8 is connected to the V- voltage through bias resistors R12 and R28. An RF bypass capacitor C10 connects between the emitter and ground terminal 24. The base of the transistor is connected to a regenerative feedback network including a feedback winding W2 of transformer T2, diode D2, which rectifies the RF energy induced in the winding W2 together with a charging capacitor C7 connected between the diode D1 and terminal 22. Resistors R11 and R20 are connected from a mutual connecting point with diode D1 and capacitor C7 to control terminal 21 and a control diode D2 is connected between a mutual connecting point with resistors R11 and R20 and to the V- voltage via resistor 28.

Oscillator circuit 200 will oscillate when terminal 21 is at ground or zero potential either via contacts 101 and switch 102 or via the conduction of transistor TR7. When terminal 21, connected to resistor R20, is at ground or zero potential the feedback network has sufficient RF energy to enable the resonant circuit to sustain oscillations. More specifically, when terminal 21 is at ground diode D2 is back-biased and cannot conduct. This establishes a timing circuit of C1 and R11 plus R20, the capacitor being charged by RF energy rectified by diode D1 which will produce sufficient energy in the feedback network to sustain oscillations. However, when terminal 21 is not grounded diode D2 will conduct and, with only R11 and C7 forming the timing circuit for the feedback network, then there is insufficient RF energy available to sustain oscillations and the resonant circuit will continue to oscillate and induce RF power into winding W3 of the driver circuit. Under these conditions the potential at terminal 21 via diode D2 and resistor R20 is at the V-- voltage and transistor TR7 will now conduct each time transistor TR5 conducts and cut off each time transistor TR5 cuts off. In this way the flipflop circuit operates continuously when either relay 101 or 105 is actuated but during the cut 1 mode the control multivibrator is disabled since its collector is grounded via contacts 100 and switch 102.

Referring to FIG. 4, there is shown a conventional push-pull amplifier 30. The amplifier 30 has three serially connected transistor amplifier stages on each side consisting of transistors TRl, TR2 and TR3 on one side and transistors TR4, TR10 and T'Rll on the other side. The amplifier 30 operates as a power amplifier to amplify the RF energy or power generated by the RF generator 20. The power amplifier is driven relatively hard by the driver amplifier to achieve the desired performance.

Referring to FIG. 5, the power supply 40 includes input terminals 41 and 42 with an AC electric power source signal generator 200 connected thereacross. The AC electric power source may, for example, be a conventional 1 l5-volt 60-cycle power source into which the power supply 40 is connected. The power supply 40 also includes a conventional power control circuit 199 for varying the AC input by changing the phase and amplitude thereof and is commercially sold by General Electric Co. as G.E. TRlAC No. 510033. This circuit includes a triac element 201 and a diac or double-based diode element 202 connected to the control electrode of the triac element 201. A pair of terminals 43a, 44 are provided for selectively connecting a variable resistor 203 into the power control circuit 199 to change its output for the coagulation" mode, and similarly a pair of terminals 43b and 45 selectively connect a variable resistor 204 into the power control circuit 119 to change its output during the "cut mode. Resistors 203 and 204 are located on the control panel and are preset according to the desired power for either mode. The terminals 43a and 44 are shown as stationary contacts which are closed by a movable contact arm of the relay 105 which is selectively energized for the "coagulate" mode. Similarly, the terminals 43b and 45 shown as stationary contacts of relay 101 are selectively closed by a contact arm 59 movable in response to the energization of the relay 101 for the "cut" mode as shown in FIG. 1. The power control circuit 199 is also adjustable by means of the variable resistor 205 to vary the output of the power supply.

Included in the power supply is a transformer 206 which couples the out ut of the power source 200 to a diode bridge 207 to provide B- DC voltage across terminals 47 and 48, and a transformer 208 couples the output of the power control 199 to a diode bridge 209 to provide the V DC voltage across terminals 46 and 47. A power switch 211 located on the control panel connects the input power from the supply 200 to the power control 199 and a lamp L1 serves to indicate when the power is on to the power supply. A capacitor 212 is connected across terminals 47 and 48 for filtering of the 60-cycle power and a resistor 213 and capacitor 214 are connected across terminals 46 and 47, the latter also being used to filter the 60- cycle power to assist in prevention of its being applied to the electrodes. In this way the waveform of the energy produced by the RF generator is not appreciably amplitude modulated by the 60-cycle power source 200. Vacuum tube type generators previously used for the cutting of tissue provide an amplitude modulated waveform which is modulated by the 60- cycle input power line to the extent of being completely modulated at 120 cycles. The effect of such amplitude modulation is to provide a series or envelopes of RF energy oscillations which decrease to substantially zero amplitude at one point in each repetition thereof.

In operation, the electrosurgical apparatus of the present invention as shown in FIG. 1 is in situ with the active electrode 1 positioned to operate on a patient represented at 220. The indifferent electrode or patient ground plate 103 is placed in situ against the body of the patient usually with the patient lying on the plate 103. The power supply switch 211 is turned on and resistors 203 and 204 are set to the desired power levels. To perform a cut, the cut switch 102 would then be closed for the cut 1" mode. The treadle switch 127 would be switched to the cut" mode, by the surgeon, thereby connecting the movable contact arm of the switch 127 to its fixed contact 128 as shown. Thus, the relay 101 is energized closing the terminals 43b and 45 of the power supply 40 and closing switch 100 to ground terminal 21 of the RF generator to turn the RF generator 20 on" to produce a high frequency electric energy in an oscillatory waveform of substantially constant amplitude as represented at C in FIG. 7. This RF electric energy is then amplified by the power amplifier 30 and transformer-coupled to the electrodes 115 and 103. The RF energy then flows from the active electrode 1 15 for selectively cutting the body tissue of the patient 220 and the energy returns to the plate 103. The RF energy, after passing into the plate 103, is then dissipated in RF chokes 121, 124 and 125.

After each cutting operation, or periodically in the process of cutting or surgery, it is necessary to coagulate the blood flowing from the cut tissues. This is accomplished by operating the treadle switch 127 thereby to switch the movable contact arm thereof to fixed contact 129. Relay 101 is de-energized while relay is energized. Thus, contacts 100 open and terminal 21 is no longer grounded and contacts 104 close terminals 12 and 13 of control multivibrator 10 to connect capacitor C30 in parallel with C5. Also the terminals 430 and 44 of the power supply 40 are closed so that a higher level of power is generated by the power supply 40 across output terminals 46 and 47. In the "coagulate" mode the potential at terminals 11 and 21 alternately changes between two different electric potential levels with each level being of a selected duration which is established by the duty or timing cycle of the flip-flop circuit, and these potential or voltage levels in turn regulate the time on and time off for the oscillator circuit 20b. Thus the voltage waveform at the output of the control multivibrator 10 may be represented by a pulse-shaped waveform B as shown in FIG. 7. The voltage or potential level to turn the oscillator circuit on is zero or ground and this occurs as above described each time transistors TRS and TR7 conduct. However, when transistor TRS cuts off then transistor TR7 in turn cuts off and the potential at terminals 11 and 21 are a V- voltage supplied via resistors 28, diode D2 and R20 and this results in shutting the oscillator circuit off until TR7 again conducts as above described. Thus the RF energy in the form of a series or envelope of oscillations are generated by generator 20 as represented at E in FIG. 7 for each on-time for transistors TRS and TR7, this RF energy or electric power being amplified by the power amplifier 30 and applied to electrodes and 103. This RF electric energy may be characterized as envelopes or packets of a relatively short duration and recurring at regular intervals and operates through the active electrode 115 to coagulate the blood flowing from the severed blood vessels along previously cut body tissue.

A third mode in which this apparatus may be used is called cut 2 and in actuality is a mode whereby the active electrode 115 both cuts and coagulates. 1n the cut 2 mode the treadle switch 127 may remain in the cut position to retain the energization of relay 101 and the cut power at terminals 46 and 47; however, switch 102 is placed in the cut 2" position which opens the ground circuit to terminal 2]. In this way the control multivibrator 10 controls the enabling or on-time for the RF generator 20 and the disabling or off-time for the RF generator in the same manner as above described with reference to the "coagulate" mode. However terminals 12 and 13 of the control multivibrator 10 are open and capacitor C30 is removed so that the on-time is longer and the off-time is shorter as represented by waveform A in FIG. 7. The RF generator will then produce a series of envelopes of RF energy oscillations of a longer duration with shorter time intervals between each series, said energy being amplified and applied to the electrodes 115 and 103. This RF energy on the active electrode 115 efi'ects partially a cutting and partially a coagulating action on the body tissue of the patient 220.

Reference is now made to the waveforms of FIG. 7 to explain the advantages of the present invention: The electrical resistance of the body tissue through which the RF current flow is essentially a resistance impedance and therefore the waveforms of the RF current, RF voltage and instantaneous RF power or energy are essentially the same as represented by waveform C, and may be characterized by being oscillatory and of a substantially constant amplitude. A preferred frequency of this RF energy is 0.5Ml-lz so that the period of each cycle is the reciprocal of the frequency or equal to 2 microseconds. The duration of the "on-time" and the coagulate mode" is about l0 microseconds an a time interval of the off-time of about 40 microseconds or a l-to-4 ratio has been found to provide excellent blood coagulation results. Accordingly, this produces a series of oscillations of RF electric energy of the same duration and recurring at regular intervals as represented by waveform E. The terms envelope" or Packet as used herein are therefore intended to refer to a series of RF energy oscillations which occur during a particular duration or preselected time interval. Since the oscillations i .3, produced by generator 20 are of a substantially constant amplitude, the positive and negative peaks define a rectangular area which may be considered an essentially rectangular shaped envelope of RF energy. This is to be distinguished from an RF energy produced by a spark-gap type generator which has damped oscillations and the instantaneous power of which decreases rapidly as represented in FIG. 7 by waveform G.

The significance of the difference between the two is best understood by considering the average power waveforms for the two types of generators as represented by wavefomis F and H. The generator 20 producing a series or envelopes of RF power E has an essentially flat average power characteristic over the duration of the envelope as represented at F, whereas that of the spark gap-type generator rapidly decreases to zero along a parabolic shaped curve of progressively decreasing slope as represented at H. Therefore in order to provide equivalent average power over a similar duty cycle, the spark-gap generator requires considerably higher RF voltages and currents.

Comparative tests have shown that the instrument above described will operate at about 2,400 volts peak-to-peak at the active electrode whereas a comparable spark-gap type generator requires about 6,500 volts peak-to-pealt. This difference in operating voltages is an important factor from the standpoint of the safety of the patient, personnel and surgeon. Further, the AC power input to the vacuum tube type oscillator generator is usually on the order of 1,000 volts at 60 cycles as compared to the 1 l7 volts for the cut 1 mode in the present apparatus and the DC power of about I ,000 volts for the vacuum tube type generator as compared to the maximum of I80 volts in the exemplary apparatus.

The average power of the exemplary apparatus to meet cutting power and peak coagulating power requirements is about 500 watts and 700 to 800 volts maximum or peak. The output of the RF generator 20 of the exemplary apparatus is in the range of about -300 volts for the cut 1 mode and about 0-400 volts for the cut 2 and coagulate modes. In turn, the output voltage at the active electrode is in the range of about 0-1 .1 KV for the cut 1" mode and about 0-l .5 KV for the cut 2 and coagulate modes. These ratings compare to a peak voltage for coagulate in the spark-gap generator of about 4.5 KV and peak power ofabout 6.5 KW.

In addition, the solid state elements employed herein provide a circuit of much improved reliability and efficiency and closer power regulation over high frequency electrosurgical instruments heretofore provided. The relatively low DC voltage of l4 volts used as the bias voltage for the transistors and for the treadle switch I27 which is preferably explosion proof" adds to the safety. in the above described circuitry the DC voltage and 60-cycle power line voltage are efi'ectively isolated from the electrodes to minimize modulation of the main power 60-cycle frequency which would otherwise affect the RF generator output and for patient safety.

Although the present invention has been described with a certain degree of particularity, it is understood that the present invention has been made by way of example and that changes in details of structure may be made without departing from the spirit thereof.

What is claimed is:

l. A method for high frequency electric surgery comprising the steps of:

generating a continuous periodic waveform of high frequency electric energy wherein within each period of the waveform of the order of tens of microseconds there is at least one burst of substantially constant amplitude oscillations of high frequency electric energy with the duration of the burst being a predetermined fraction of the period of the waveform; and continuously applying the generated energy to a body site where a surgical change is desired in said body site. 2. A method as set forth in claim 1 wherein said electric energy is oscillating at a frequenc of about 0. SMl-lz.

3. method as set forth in c aim I wherein the bursts of high frequency electric energy are about 10 microseconds in duration and the time interval between bursts is about 40 microseconds.

4. A method as set forth in claim 1 wherein the bursts of high frequency electric energy are about 15 microseconds in duration and the time interval between the bursts of energy is about 20 microseconds.

5. The method of claim 1 wherein said predetermined fraction is in the order of one fourth, and the generated energy is continuously applied to said body site when it is desired to coagulate the blood flowing from said body site.

6. The method of claim 1 wherein said predetermined fraction is in the order of four sevenths.

7. Electrosurgical apparatus comprising: generator means for generating a continuous periodic waveform of high frequency electric energy wherein within each period of the wavefonn there is at least one burst of substantially constant amplitude oscillations of high frequency electric energy with the duration of the burst being a fraction of the period of the waveform;

selective control means including an assymetrical waveform generator for selectively controlling said generator means to change the fraction of the period in accordance with a desired surgical procedure;

user operable means for switching on and off when desired,

said generator means; and

electrode means coupled to said generator means for application of the electric energy generated.

8. The invention recited in claim 7 wherein said generator means is operable to generate RF energy.

9. The invention recited in claim 7 wherein said electrode means includes:

an indifferent electrode positioned against a body upon which surgery is to be performed, and

an active electrode positioned for selectively applying the high frequency electric energy generated to said body.

10. The invention recited in claim 7 wherein said generator means includes an RF oscillator circuit having a resonant circuit and feedback network to sustain oscillations in the resonant circuit, said oscillator circuit being turned off by said control multivibrator by disabling said feedback network.

ll. The apparatus of claim 7 and including means for changing the degree of assymetry of the assymetrical waveform.

t i i i i 

1. A method for high frequency electric surgery comprising the steps of: generating a continuous periodic waveform of high frequency electric energy wherein within each period of the waveform of the order of tens of microseconds there is at least one burst of substantially constant amplitude oscillations of high frequency electric energy with the duration of the burst being a predetermined fraction of the period of the waveform; and continuously applying the generated energy to a body site where a surgical change is desired in said body site.
 2. A method as set forth in claim 1 wherein said electric energy is oscillating at a frequency of about 0.5MHz.
 3. A method as Set forth in claim 1 wherein the bursts of high frequency electric energy are about 10 microseconds in duration and the time interval between bursts is about 40 microseconds.
 4. A method as set forth in claim 1 wherein the bursts of high frequency electric energy are about 15 microseconds in duration and the time interval between the bursts of energy is about 20 microseconds.
 5. The method of claim 1 wherein said predetermined fraction is in the order of one fourth, and the generated energy is continuously applied to said body site when it is desired to coagulate the blood flowing from said body site.
 6. The method of claim 1 wherein said predetermined fraction is in the order of four sevenths.
 7. Electrosurgical apparatus comprising: generator means for generating a continuous periodic waveform of high frequency electric energy wherein within each period of the waveform there is at least one burst of substantially constant amplitude oscillations of high frequency electric energy with the duration of the burst being a fraction of the period of the waveform; selective control means including an assymetrical waveform generator for selectively controlling said generator means to change the fraction of the period in accordance with a desired surgical procedure; user operable means for switching on and off when desired, said generator means; and electrode means coupled to said generator means for application of the electric energy generated.
 8. The invention recited in claim 7 wherein said generator means is operable to generate RF energy.
 9. The invention recited in claim 7 wherein said electrode means includes: an indifferent electrode positioned against a body upon which surgery is to be performed, and an active electrode positioned for selectively applying the high frequency electric energy generated to said body.
 10. The invention recited in claim 7 wherein said generator means includes an RF oscillator circuit having a resonant circuit and feedback network to sustain oscillations in the resonant circuit, said oscillator circuit being turned off by said control multivibrator by disabling said feedback network.
 11. The apparatus of claim 7 and including means for changing the degree of assymetry of the assymetrical waveform. 